Metrology methods to detect plasma in wafer cavity and use of the metrology for station-to-station and tool-to-tool matching

ABSTRACT

A process chamber for detecting formation of plasma during a semiconductor wafer processing, includes an upper electrode, for providing a gas chemistry to the process chamber. The upper electrode is connected to a radio frequency (RF) power source through a match network to provide RF power to the wafer cavity to generate a plasma. The process chamber also includes a lower electrode for receiving and supporting the semiconductor wafer during the deposition process. The lower electrode is disposed in the process chamber so as to define a wafer cavity between a surface of the upper electrode and a top surface of the lower electrode. The lower electrode is electrically grounded. A coil sensor is disposed at a base of the lower electrode that extends outside the process chamber. The coil sensor substantially surrounds the base of the lower electrode. The coil sensor is configured to measure characteristics of RF current conducting through the wafer cavity. The characteristics of the RF current measured by the coil sensor are used to confirm presence of plasma within the wafer cavity.

FIELD OF THE INVENTION

The present embodiments relate to semiconductor equipment tools, andmore particularly, to process chambers used for deposition of materiallayers over semiconductor wafers, and metrology systems and methods fordetecting when plasma is present in a cavity of the process chamber.

BACKGROUND Description of the Related Art

Atomic Layer deposition (ALD) is a plasma deposition technique that isused to deposit thin films of deposition chemistry on a substrate, suchas a semiconductor wafer. The ALD is performed by exposing a surface ofthe semiconductor wafer to alternate gaseous deposition chemistries. Thegaseous deposition chemistries are inserted into an ALD chambersequentially in a non-overlapping manner to allow thin films to growuniformly on the surface of the semiconductor wafer. To enableapplication of gaseous deposition chemistries, ALD systems may include avaporizer to convert each of the deposition chemistries in liquid formto gaseous form in a controlled manner and deliver the gaseous form ofthe deposition chemistries to the ALD chamber during deposition process.When applied on a surface of the semiconductor wafer (or simply referredto as the “wafer”), molecules of a gaseous deposition chemistry reactwith the wafer surface to form a thin film.

Chambers used for ALD process include wafer-receiving mechanisms, suchas pedestals, electrostatic chucks (ESCs), etc., for supporting thesemiconductor wafer during processing, and an upper electrode forproviding gaseous deposition chemistries into the chamber. The pedestalor ESC acts as a lower electrode. The upper electrode and the pedestalare made of a conductive material that is capable of withstanding hightemperatures that exist within the process chambers during a depositionprocess.

Thin film deposition can be achieved using a plasma in an ALD chamber,for example. The species (i.e., deposition chemistries) are energized inthe plasma and the energized species help to induce reactions withfeatures formed on a surface of the wafer. In an ALD chamber, plasma isgenerated by applying radio frequency (RF) power to excite the gaseousform of the deposition chemistry supplied to the ALD chamber. The RFpower is provided by a RF power source through the upper electrode ofthe ALD chamber.

Metrology tools are used to measure the RF characteristics of the RFpower supplied to the ALD chamber. Some of the RF characteristics thatare measured include RF voltage and total current. A common metrologytool used is a voltage-current (VI) probe. The VI probe is typicallylocated close to where the RF power is input to the RF powered upperelectrode. However, because of its location (i.e., proximity to theinput of the powered upper electrode), the VI probe measures a sum ofthe current passing into the ALD chamber, e.g., the current related toparasitic plasma and parasitic capacitive coupling to ground. Since theVI probe measurement is made proximate to the input, the measurementwill not identify if plasma has been generated between the upperelectrode and the wafer surface (i.e., in the wafer cavity).

Determining whether plasma is present in a wafer cavity is especiallycritical for any chamber that does not provide visual or optical accessto the wafer cavity. Without the visual or optical access, one needs torely on the existing metrology tools to correctly identify when plasmais present. Unfortunately, using existing metrology tools (i.e., VIprobes), it is very hard to reliably confirm ignition of plasma in thewafer cavity. The problem is further exacerbated when the parasiticcapacitance detected in the chamber is comparable to the capacitance ofthe wafer cavity.

It is in this context that embodiments of the invention arise.

SUMMARY

Embodiments of the invention define a process chamber that employs ametrology process and tool setup for confirming plasma ignition within awafer cavity defined in the process chamber. The process chamberincludes an upper electrode and a lower electrode. A wafer cavity isdefined in a region between the upper electrode and the lower electrodeof the process chamber and is where plasma is usually formed.

The upper electrode is used to supply deposition chemistries to thewafer cavity and the lower electrode acts as a wafer-receiving mechanismfor receiving and supporting a semiconductor wafer during depositionprocess. The lower electrode, in some implementations, is in the form ofa pedestal and the upper electrode acts as a showerhead. The upperelectrode is coupled to an RF power source through a match network. TheRF power source provides the power to ignite a plasma within the processchamber. In one embodiment, an RF metrology tool, such asvoltage-current (VI) probe, is disposed between the RF power source andthe upper electrode, and is near an RF power input to the processchamber. The VI probe is used to detect and measure RF characteristics,such as RF voltage and current. Using these measurements, othercharacteristics can be identified, such as impedance, RF power deliveredto the process chamber, etc.

In one embodiment, the process chamber is further configured with a coilsensor, which is usable to measure conductance current of a plasma, whenformed in the wafer cavity of the process chamber. In this embodiment,the coil sensor is disposed at a base of the lower electrode thatextends outside of the process chamber. For example, the coil sensor isconfigured to substantially surround a base of the lower electrode. Thelocation of the coil sensor enables the coil sensor to measurecharacteristics of RF current conducting through the wafer cavity. Inone embodiment, the RF current measured by the coil sensor excludes RFcurrent generated due to parasitic plasma and, in some instances,parasitic capacitance to ground. The RF characteristics detected by thecoil sensor can be used to correctly confirm ignition of plasma in thewafer cavity, as will be described in more detail below. Accordingly,the coil sensor, along with the VI probe, defines a metrology system andmethod for confirming the presence of plasma in the wafer cavity.

In one embodiment, a process chamber for detecting formation of plasmawithin a wafer cavity during a semiconductor wafer processing, isdisclosed. The process chamber includes an upper electrode with aplurality of inlets for supplying a gas chemistry to the processchamber. The upper electrode is connected to a radio frequency (RF)power source through a match network to provide RF power to generate aplasma. The process chamber also includes a lower electrode forreceiving and supporting the semiconductor wafer during the depositionprocess. The lower electrode is disposed in the process chamber suchthat a wafer cavity is defined between a surface of the upper electrodeand a top surface of the lower electrode. The lower electrode iselectrically grounded. A coil sensor is disposed at a base of the lowerelectrode that extends outside the process chamber. The coil sensorsubstantially surrounds the base of the lower electrode. The coil sensoris configured to measure characteristics of an RF current conductingthrough the wafer cavity. Other currents due to parasitic plasma and/orparasitic capacitive coupling to ground are, in one embodiment, notmeasured by the coil sensor. The RF current measured by the coil sensoris used to confirm presence of plasma within the wafer cavity.

In one embodiment, the process chamber further includes a VI probe isdisposed outside the process chamber between the RF power source and theupper electrode to measure characteristics of the RF power delivered tothe process chamber.

In another embodiment, a process chamber is disclosed. The processchamber includes an upper electrode coupled to a radio frequency (RF)power supply. The process chamber further includes a lower electrodecoupled to ground. A wafer cavity is defined between the upper electrodeand the lower electrode. A base is coupled to the lower electrode. Thebase is configured to extend into the process chamber from below theprocess chamber. The base has an inner portion that is inside theprocess chamber and an outer portion that is outside the processchamber. A circular channel is defined around the outer portion of thebase. A coil sensor is disposed in the circular channel so that the coilsensor substantially surrounds the outer portion of the base. A firstend of the coil sensor is connected to an input-output controller and asecond end of the coil sensor is proximate to the first end when thecoil sensor is disposed in the circular channel.

In one embodiment, a method for measuring operational parameters of aprocess chamber is disclosed. The method includes operating the processchamber using a first power level that is lower than a power required toignite a plasma in a wafer cavity of the process chamber. A firstcurrent value conducting through a base of a lower electrode of theprocess chamber is measured for a first voltage detected in the processchamber during operation of the process chamber with the first powerlevel. The process chamber is operated using a second power level thatis lower than the power required to ignite the plasma in the wafercavity. The second power level is higher than the first power level. Asecond current value conducting through the base of the lower electrodeof the process chamber is measured for a second voltage detected in theprocess chamber during operation of the process chamber with the secondpower level. Using the first and the second voltage and the first andthe second current value measurements, a determination is made for whenplasma is ignited in the wafer cavity during a plasma process operationthat is run using a process power level that is higher than the firstpower level. A process current value conducting through the base of thelower electrode is measured for a process voltage detected in theprocess chamber during the plasma process operation with the processpower level and the determination when the plasma is ignited in thewafer cavity is made during the plasma process operation based on acomparison of the process voltage and the process current value againstthe first and second voltages and the first and the second currentvalues.

Embodiments of the disclosure provide a metrology system for confirmingplasma ignition within the wafer cavity of a process chamber used forprocessing the wafer. In a process chamber that does not include avisual or an optical access, correctly identifying plasma ignition isvery useful as it allows confirmation of proper chamber operation. Themetrology system includes a coil sensor that is wrapped at leastpartially around a base of the lower electrode that extends outside ofthe process chamber. The location of the coil sensor enables the coilsensor to measure the RF current conducting through the wafer cavity andthe lower electrode to ground. The measured RF current is used toreliably confirm ignition of plasma in the wafer cavity.

Other aspects of the invention will become apparent from the followingdetailed description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 illustrates a simplified block diagram of a wafer process chamberused in a deposition process to form thin films on a surface of a wafer,in one embodiment of the invention.

FIG. 2A illustrates an expanded view of a base of a lower electrodeillustrated in FIG. 1, in one embodiment of the invention.

FIG. 2B illustrates a cross section view of a coil sensor used in FIG.2A, in one embodiment of the invention.

FIG. 2C illustrates a simplified overhead view of the coil sensor ofFIG. 2A, in one embodiment of the invention.

FIG. 3 illustrates an example electrical model showing flow of currentthrough the process chamber, in an embodiment of the invention.

FIG. 4A-4B illustrate an example of no-plasma and plasma within a wafercavity, and use of a coil sensor to measure displacement current toverify plasma ignition, in one embodiment of the invention.

FIG. 5 illustrates an example graph of voltage detected at plasma andcoil current detected by a coil sensor, in one embodiment of theinvention.

FIG. 6 illustrates process flow operations followed for measuringoperational parameters of a process chamber, in one embodiment of theinvention.

DESCRIPTION

Embodiments of the disclosure define metrology methods and systems fordetecting RF current through a wafer cavity defined in a processchamber, which is indicative of plasma generation within the wafercavity. In some embodiments, the process chamber is used for depositionprocessing, e.g., PECVD or ALD processing. The metrology system, in oneembodiment, includes a coil sensor that is provided at a base of a lowerelectrode, outside of the process chamber. The current detected by thecoil sensor is used to confirm plasma ignition in the wafer cavity.

In one embodiment, the process chamber includes an upper electrode thatis connected to an RF power source and a lower electrode that iselectrically grounded. A wafer cavity is defined in a region between theupper electrode and the lower electrode. The wafer cavity represents aprocess region within the process chamber where a plasma is usuallyformed and a surface of a semiconductor wafer (or simply a “wafer”) isprocessed. During a deposition process, plasma is ignited in the wafercavity using the gas chemistry and the RF power provided by the upperelectrode and the surface of the wafer is exposed to the plasma.

A voltage-current (VI) probe is disposed outside the process chamberbetween the RF power source and the upper electrode. The VI probe isused to measure RF characteristics of the RF power at the powered upperelectrode. The RF characteristics measured by the VI probe includes thecurrent conducting through the wafer cavity and the current through anyparasitic plasma and/or parasitic capacitive coupling to ground. In someembodiments, the VI probe provides data used to calculate a phasedifference related to the measured voltage and current. Capacitivecoupling occurs when a gap is present between two conductive componentsthrough which current can pass. For example, capacitive coupling occursin the process chamber due to current passing through a gap between thepowered upper electrode and the lower electrode, which is electricallygrounded. Similarly, capacitive coupling occurs due to current passingthrough a gap between the powered upper electrode and a wall of theprocess chamber that is electrically grounded. Such capacitive couplingis deemed “parasitic” as the current is not intended to pass throughthese components. As the parasitic capacitance becomes comparable withthe capacitance of the wafer cavity, it becomes increasingly harder toconfirm ignition of plasma within the wafer cavity by just relying onthe RF characteristics measurements provided by the VI probe alone.

In order to accurately determine onset of the plasma within the wafercavity, a coil sensor is disposed at a base of the lower electrode thatextends outside of the process chamber. The coil sensor partially orsubstantially surrounds the lower electrode. The coil sensor isconfigured to detect RF current conducting through the wafer cavity andthe lower electrode to ground. The current detected by the coil sensoris therefore used to confirm ignition of plasma in the wafer cavity.

It should be appreciated that the present disclosure can be implementedin numerous ways, such as a process, an apparatus, a system, a device,or a method. Several embodiments will now be described with reference tothe drawings.

Thin film deposition is implemented in an atomic layer deposition (ALD)system, a plasma-enhanced chemical vapor deposition system (PECVD), etc.Different forms of ALD or PECVD system can be employed for performingthin film deposition. For example, the ALD or the PECVD system mayinclude one or more process chambers or “reactors” with each processchamber housing one or more wafers for wafer processing. In someimplementations, each process chamber may include one or more stations,with each station housing a wafer. Each process chamber or each stationin a process chamber may have receiving and holding mechanism to receiveand hold the wafer in a defined position with or without motion (e.g.,rotation, vibration, agitation, etc.) within that position. In an ALDsystem, for example, a plurality of deposition chemistries are appliedin a sequential manner to the surface of the wafer in a uniform way soas to deposit multiple layers of thin film on the wafer surface. As aresult, the multiple layers of thin film deposition may all occur in onestation of a process chamber or each film deposition may occur at adifferent station of the process chamber. In a PECVD system, forexample, each station of a process chamber (in a multi-station processchamber) may be used to deposit a thin film on the surface of adifferent wafer. The various implementations of the disclosure aredescribed with reference to the use of a metrology system in either anALD system or a PECVD system. However, such implementations are notrestricted to the ALD or the PECVD system but may be extended to otherdeposition systems, where accurate measurement of process parameters isneeded.

FIG. 1 illustrates a simplified block diagram of an example processchamber 102 used to process a wafer 100, in one embodiment. The processchamber 102 includes one or more chamber walls, an upper electrode 154and a lower electrode 110. The chamber wall is electrically grounded.The upper electrode 154 is electrically coupled to a RF power source 150through a match network (not shown). A voltage-current (VI) probe 152 isdisposed outside the process chamber 102 between the RF power source 150and the upper electrode 154 and is used to measure RF characteristics ofRF power provided to the process chamber 102 through the upper electrode154. In some implementations, the VI probe 152 is disposed proximal toan RF input to the upper electrode 154. The VI probe 152 may include adistinct voltage sensor (not shown) and a current sensor (not shown).The upper electrode 154 also functions as a showerhead, as it providesgasses into the process chamber 102.

In some implementations, the upper electrode 154 is made of a conductivematerial, such as aluminum or aluminum nitride. In one implementationwhere the upper electrode 154 is made of aluminum nitride, the upperelectrode 154 may have an additional layer of tungsten coating over thealuminum nitride. Alternately, the upper electrode 154 may be made ofceramic or any other conductive material that is capable of withstandingthe temperature and processing conditions inside the process chamber102.

The lower electrode 110 functions as a pedestal for supporting thesemiconductor wafer. The lower electrode 110, in some implementations,is electrically grounded. In some implementations, the lower electrode110 is made of a conductive material, such as aluminum or aluminumnitride. In one embodiment, a base 110 a of the lower electrode 110extends outside the process chamber 102. The lower electrode 110 can bemoved up or down depending on processing. A bellows 120 is shown tocover portions of moving parts of the base 110 a, which enable the upand down movement of the lower electrode 110.

In an alternate embodiment, a separate base 110 a may be coupled to thelower electrode 110. In this embodiment, the base 110 a is disposed atthe bottom of the process chamber 102 such that an inner portion of thebase 110 a extends into the process chamber 102 from below the processchamber 102 and an outer portion of the base 110 a is disposed outsidethe process chamber 102. The base 110 a may include moving parts thatallow the base 110 a and the lower electrode 110 coupled to the base 110a to move up or down. A bellows 120 is disposed to cover portions of themoving parts of the base 110 a.

A wafer cavity 160 is defined between the upper electrode 154 and thelower electrode 110. The wafer cavity 160 is a region in the processchamber where the deposition chemistries are introduced in gaseous formthrough a plurality of inlets defined on a surface of the upperelectrode 154 facing the wafer cavity 160, and a plasma 164 is ignitedusing RF power supplied through the upper electrode 154.

In one embodiment, a ring 156 is disposed at an outer periphery of thesurface of the upper electrode 154 facing the wafer cavity 160. The ring156 defines a pocket within the wafer cavity 160 to allow the generatedplasma 164 to be substantially contained inside the pocket. The ring156, in one implementation, is made of a ceramic material. In anotherimplementation, the ring 156 is made of any other conductive materialthat is capable of withstanding the processing conditions inside theprocess chamber 102 during the deposition process. In oneimplementation, the thickness and the depth of the ring 156 is designedso as to enable successful plasma containment.

A dielectric material 158 is disposed between the upper electrode 154and wall of the process chamber 102. The dielectric material 158provides insulation to the wall of the process chamber 102.

In one embodiment, an edge ring 111 is disposed on a top surface of thelower electrode 110. When present, the edge ring 111 is disposedimmediately adjacent to and sufficiently surrounds a wafer 100 when thewafer 100 is received and supported on the lower electrode 110. The edgering 111, in one embodiment, is made of a conductive material, such asceramic.

A coil sensor 116 is provided at a base 110 a of the lower electrode 110that extends outside the process chamber 102. A more detailedexplanation of the location of the coil sensor 116, the differentcomponents of a region 5 of the process chamber 102 where the coilsensor 116 is disposed, and the components of the coil sensor 116 willbe provided with reference to FIGS. 2A, 2B and 2C. In someimplementations, the coil sensor 116 is an induction coil-based sensorthat is disposed to partially or substantially surround the base 110 aof the lower electrode 110. The coil sensor 116 is used to measure RFcharacteristics (e.g., RF current flowing through the wafer cavity 160)of the RF power delivered to the process chamber 102. The location ofthe coil sensor 116 at the base 110 a of the lower electrode 110 allowsthe coil sensor 116 to exclude RF current flowing through parasiticplasma. The parasitic plasma, for example, is generated in a region thatis outside of the wafer cavity 160 defined over the lower electrode 110.As a result, the RF current flows through the parasitic plasma away fromthe lower electrode 110 and is, therefore, not detected by the coilsensor 116. Similarly, the coil sensor 116, in some embodiments,excludes some of the RF current due to parasitic capacitance detected inthe process chamber 102. The parasitic capacitance, for example, occurswhen the RF current flows through a gap between the upper electrode anda wall of the process chamber 102, away from the lower electrode 110. Asa result, the coil sensor 116 does not detect the RF current that flowsthrough the wall of the process chamber 102 to ground.

In one implementation, the coil sensor 116 is coupled to an Input-Outputcontroller (IOC) 174. The IOC 174 is configured to receive signalsrelated to RF characteristics measured and outputted by the coil sensor116 and interpret the signals. In another implementation, the VI probe152 may be coupled to the IOC 174 so that RF characteristics measured bythe VI probe 152 may be provided as signals to the IOC 174. The IOC 174interprets the signals generated by the VI probe 152 to determine a baseline of measurement for the voltage measured by the VI probe 152 and thecurrent measured by the coil sensor 116 for a base power level appliedto the process chamber. Once the base line measurement is set for theprocess chamber 102, the current measured by the coil sensor 116 and thevoltage determined by the VI probe 152 for a power level that isdifferent from the base power level may be compared against the baseline measurement to determine if plasma is ignited or not in the processchamber 102. As part of interpreting the signals, the IOC 174 mayprovide appropriate information for rendering on a user interface (notshown) of a computing device (not shown) that is coupled to the IOC 174.

In some implementations, the information provided by the IOC 174 mayinclude historical measurements of the signals, an alarm message when aparticular RF characteristic extends outside a window of acceptableparameter, etc. As the IOC 174 receives output signals from the coilsensor 116 in-situ during the deposition process, the output signalsreflect current process conditions within the wafer cavity 160. As aresult, analyzing the current process conditions would provide aninsight into presence of plasma in the wafer cavity 160 and what RFcharacteristics provide consistently successful indication of plasmaignition in the wafer cavity 160. For example, the current processconditions detected in the process chamber 102 may indicate that eitherthe plasma was not ignited in the wafer cavity 160 or the density of theplasma was too low to perform a successful deposition process. Suchprocess conditions would lead to less than optimal deposition processwithin the process chamber. As a result, as part of the analysis,current process conditions may be compared against the historicalmeasurements that resulted in successful deposition process to determinewhich parameter needs to be adjusted to produce a level of plasma thatresults in an optimal wafer deposition process. This process can be usedfor assessing the process conditions for station-to-station matching aswell as tool-to-tool matching.

In some implementations, the RF characteristics measured by the coilsensor 116 and the VI probe 152 are used to measure two sets of outputs.In some implementations, the two sets of RF characteristics measured bythe coil sensor 116 and VI probe 152 are transmitted to the IOC 174 asoutput signals and the IOC 174 processes the output signals anddetermines whether plasma is ignited or not ignited in the wafer cavity160. The first set of output relates to a base reading 174 a of the RFcharacteristics and the second set of output relates to an operatingplasma reading 174 b. In one implementation, the first set of output mayinclude at least two RF characteristics measurements and the second setof output may include at least one RF characteristics measurement.Detection of the base reading 174 a and using the base reading 174 a todetermine plasma ignition within the wafer cavity 160 will be describedin more detail with reference to FIG. 5.

In one implementation, a small amount of RF power 150 is supplied to thewafer cavity 160 and the coil sensor 116 is used to measure the RFcharacteristics for the supplied RF power 150. The measured RFcharacteristics represent a first reading for the first set that is partof the base reading measurement 174 a. For example, the coil sensor 116may measure the RF current flowing through the wafer cavity 160 for theapplied low RF power that corresponds to a first voltage detected in theprocess chamber and this measured RF current and first voltagerepresents a first reading of the first set of base RF current (one ofthe RF characteristics component in the base reading 174 a). Themagnitude of the first RF power provided to define the base reading isknown to not ignite plasma in the wafer cavity 160. In oneimplementation, the first RF power supplied to obtain base readingmeasurement is less than 150 W. In this implementation, the RF currentmeasured by the coil sensor is less than 6 amps. Next, a second RF poweris applied to the process chamber 102. The second RF power is also knownto not ignite plasma in the wafer cavity 160. The RF characteristics forthe second RF power are measured by the coil sensor 116 and the VI probe152. The measured RF characteristics represent a second reading of thebase reading measurement 174 a. The base reading measurement 174 a forthe process chamber 102 is maintained by the IOC 174 and is used inanalyzing subsequent RF characteristics measurements when different RFpower is applied to the process chamber 102 to determine presence ofplasma in the wafer cavity 160. In some implementations, the first setmay include RF characteristic measurements for more than two RF powerlevels and the base reading measurement 174 a may be determined usingthe measured RF characteristics of the different RF power levels.

Once the base reading measurements 174 a for the RF characteristics(e.g., voltage, current) is established using the first set of readings,a second set of RF characteristic measurements is obtained by the coilsensor 116 and the VI probe 152 for a third RF power supplied to theprocess chamber 102. The third RF power supplied to the process chamber102 to obtain the second set of RF characteristics may be different fromthe RF power that was used to generate the base line measurement 174 a.The second set of RF characteristics measured by the coil sensor 116includes the RF current flowing through the wafer cavity and the RFcharacteristics measured by the VI probe 152 includes at least thevoltage and the phase difference between current and voltage.

In order to confirm ignition of plasma 164 in the wafer cavity 160 thesecond set of RF characteristics measurement is compared against thefirst set of RF characteristics measurement representing base linereading 174 a. Based on the comparison, it can be determined that plasmais either ignited or not ignited in the wafer cavity 160. When it isdetermined that plasma is ignited in the wafer cavity 160, the measuredRF characteristics of the second set correspond to operating plasmareading 174 b.

The IOC 174 uses the result of the comparison to generate appropriateinformational message for rendering at the user interface.

FIG. 2A illustrates a magnified cross-sectional view of a lower portion5 of the process chamber 102 showing the base 110 a of the lowerelectrode 110 wherein a coil sensor 116 is installed, in one embodiment.In one embodiment, the base 110 a of the lower electrode 110 where thecoil sensor 116 is disposed is located outside of the process chamber102. The base 110 a of the lower electrode 110 includes moving partsthat allow the lower electrode 110 to be moved up or down depending onprocessing of wafer. Portions of the moving parts at the base 110 a ofthe lower electrode 110 are covered by bellows 120. A dielectricinsulator 112 is provided immediately adjacent to the base 110 a of thelower electrode 110. The dielectric insulator 112 protects adjacentstructures of the process chamber 102 by providing sufficient insulationfrom the RF power flowing through the lower electrode 110. An aluminumclamp 118 is provided immediately adjacent to the dielectric insulator112. The aluminum clamp 118, in some embodiments, is provided to holddifferent parts associated with the lower electrode 110 and/or theprocess chamber 102 together. An O-ring 114 is provided in a regiondefined between the aluminum clamp 118 and the dielectric insulator 112.In one embodiment, the O-ring is made of dielectric material. The O-ring114, in some embodiments, acts to seal any gaps between the dielectricinsulator 112 and the aluminum clamp 118. A coil sensor 116 is disposedbetween the O-ring 114 and the aluminum clamp 118 of the process chamber102. In some embodiments where the O-ring 114 is not present, the coilsensor may be disposed adjacent to and either partially or substantiallysurrounds the base 110 a of the lower electrode 110.

In one embodiment, a circular channel is defined around the base 110 aof the lower electrode 110. In this embodiment, the coil sensor 116 isdisposed in the circular channel so as to substantially surround thebase 110 a of the lower electrode 110. The coil sensor 116 is disposedwithin the circular channel such that a first end of the coil sensor 116is proximate to a second end of the coil sensor 116. In one embodimentthe first end of the coil sensor 116 is connected to an input-outputcontroller (IOC) so that the measurements from the coil sensor 116 canbe transmitted to the IOC. Based on the location where the coil sensor116 is disposed, the coil sensor 116 is able to accurately measure theRF characteristics for the RF current conducting through the wafercavity 160 during a deposition process, to correctly confirm presence ofplasma within the wafer cavity 160.

FIG. 2B illustrates a cross-section of a coil sensor 116 used to confirmpresence of plasma in the wafer cavity 160, in one embodiment. The coilsensor 116, in one embodiment, is an annular-shaped Rogowski coil andincludes a helical coil of wire with an inner conductor 116 a goingthrough a center of a dielectric material provided therein and returningas a wrapping conductor 116 b wrapped around the dielectric material, sothat both a first end and a second end of the wire are at the same endof the coil. The annular-shaped coil sensor 116 is disposed tosubstantially or partially surround the base 110 a of the lowerelectrode 110 so as to measure RF current conducting through the wafercavity and the lower electrode 110 toward ground. The coil sensor 116further includes a heat shrink tube disposed outside of the helical coilof wire to provide insulation to the conductive wire contained within.An RF sleeve is disposed outside the heat shrink tube to hold thevarious components of the coil sensor 116 together. The coil sensor, inone embodiment, is flexible such that the coil sensor can be insertedinto a circular channel defined at a base 110 a of the lower electrode110. In one embodiment, the coil sensor is connected to a coaxialconnector 121, which in turn is connected to the IOC (not shown) so thatthe signal transmission from the coil sensor is transmitted through thecoaxial connector 121 to the IOC.

FIG. 2C illustrates a top view of the coil sensor 116. As shown, thecoil sensor 116 includes an inner conductor 116 a to detect the RFcurrent flowing through the lower electrode 110 and a wrapping conductor116 b that is connected to an input-output controller (IOC) (not shown)through a coaxial connector 121. The coil sensor 116 is configured totransmit information related to the detected RF characteristics asoutput signals to the IOC.

In one embodiment, the coil sensor 116 works in the following manner. Afirst end of the coil sensor 116 detects the RF current passing throughthe wafer cavity and the lower electrode. The detected RF currentinduces a voltage in the coil sensor 116 that is proportional to thedetected RF current. A second end of the coil sensor 116 is connected toan input-output controller (IOC) and the voltage output from the coilsensor 116 is provided to the IOC as an output signal. The IOC receivesand interprets the output signal, analyzes the interpreted output signaland generates appropriate information for rendering on a user interfaceat a display screen (i.e., display device) of a computing device (notshown) that is communicatively connected to the IOC.

It should be noted that the Rogowski coil is one type of currenttransformer that can be used to measure the RF characteristics for thecurrent conducting through the wafer cavity. The embodiments are notrestricted to the use of Rogowski coil but may employ other types ofcurrent transformers to measure the RF characteristics for the currentconducting through the wafer cavity.

FIG. 3 illustrates an equivalent electric circuit model of a processchamber in which a coil sensor 116 is provided, in one embodiment. Theelectric circuit model identifies various electrical components thatcorrespond to different parts of the process chamber 102. The processchamber 102, for example, may be used for performing ALD or PECVD. Avoltage-current (VI) probe 152 is coupled to an upper electrode outsidethe process chamber 102 near an RF power input 150 to measurecharacteristics of the RF power delivered to the process chamber 102through the upper electrode. A change in RF power results in a change inthe RF current flowing through the upper electrode 154. The changing RFcurrent induces a voltage in the upper electrode (which is conductive)as well as in other conductive elements within the process chamber 102.This is represented by inductance L1. The total RF current flowingthrough the process chamber flows through the inductance L1.

Capacitance C1 relates to a parasitic capacitance that is caused due tocurrent passing through a gap detected between the conductive upperelectrode and an electrically grounded wall of the process chamber.Similarly, capacitance C2 relates to a parasitic capacitance that iscaused due to current passing through a gap detected between the upperelectrode and the lower electrode. A RF current (represented asZ_plasma) flowing through the wafer cavity and lower electrode is causedby varying the RF power supplied to the process chamber. The RF currentflowing through the wafer cavity and the lower electrode flows throughthe second inductance L2. The coil sensor 116 is used to measure the RFcurrent flowing through the wafer cavity and the lower electrode. The RFcurrent measured by the coil sensor 116 is used to confirm ignition ofplasma in the wafer cavity.

Although various embodiments have been discussed with reference to achamber having a powered upper electrode and grounded base electrode,variations of these embodiments are also possible. For example, in oneembodiment, a process chamber 102 is defined wherein the upper electrode154 is electrically grounded and the lower electrode 110 is coupled to aRF power source 150 through a match network. In this embodiment, avoltage-current (VI) probe 152 is disposed outside the process chamber102 between the RF power source 150 and the lower electrode 110 and isused to measure RF characteristics of RF power provided to the processchamber 102 through the lower electrode 110. A coil sensor 116 isdisposed at the upper electrode 154 that is extending outside theprocess chamber 102 to measure the RF characteristics of the RF powerdelivered to the process chamber 102.

As in other embodiments, the coil sensor 116 is coupled to aninput-output controller (IOC) 174 to relay the signals related to the RFcharacteristics measured by the coil sensor 116. The IOC 174 processesthe signals and present appropriate information for rendering on a userinterface of a computing device that is communicatively coupled to theIOC 174.

FIG. 4A illustrates a simplified rendition of a process chamber 102during measurement of displacement current, in one embodiment. Asillustrated, the displacement current measured by the coil sensor 116 isfor non-plasma condition detected in process chamber 102. Thedisplacement current relates to parasitic current that is caused byparasitic capacitance C1 and C2 detected in the process chamber. Thedisplacement current is measured by the coil sensor 116 disposed at abase 110 a of the lower electrode 110. In some embodiments, thedisplacement current and the parasitic capacitance are used to determineother RF characteristics, such as impedance. The impedance measurementobtained from the displacement current is termed as “dark” impedance asthe measurement relates to non-plasma condition within the processchamber 102.

FIG. 4B illustrates a simplified rendition of a process chamber 102during measurement of RF current by the coil sensor 116 that confirmsplasma-on condition, in one embodiment. The RF current detected by thecoil sensor 116 includes the displacement current and conduction currentflowing through the wafer cavity 160 toward the base of the lowerelectrode 110. As noted above, the displacement current is caused byparasitic capacitance C1 and C2 detected in the process chamber 102.Knowing the value of the displacement current (e.g., typically about <6amps) for the plasma chamber 102 and the voltage detected for the RFpower applied to the plasma chamber 102, it is possible to determineplasma ignition in the wafer cavity 160. For example, plasma ignitionmay be confirmed by comparing the RF current value measured by the coilsensor 116 and the voltage value measured by the VI probe 152 against abase reading measurement established for the power level applied to theprocess chamber 102.

FIG. 5 illustrates a graph plotting voltage (due to RF power) againstcoil current (i.e., RF current) measured by the coil sensor 116 forconfirming ignition of plasma in wafer cavity 160, in one embodiment. Inone embodiment, a method is provided that enables determination of adividing line 506 (e.g., baseline), that identifies when plasma will beon in the wafer cavity 160 and no plasma will be present in the wafercavity 160, when the coil sensor 116 is implemented.

In one embodiment, the dividing line 506 is identified by conductingmeasurements when it is known that no plasma will be generated. In oneembodiment, knowledge that no plasma will be generated is based on ameasurement of phase difference (□) between voltage and current, asmeasured by the VI probe 152. For example, from experimentation, it isknown that no plasma will be generated when the phase difference isclose to −90 degrees.

In one embodiment, a first power setting is provided to the processchamber 102 by RF power source 150. This first power setting will beused to identify a first plot point 502 on graph 500. The first plotpoint 502 corresponds to voltage V₁ for the first power setting appliedto the process chamber 102, and the current sensed by the coil sensor116 (i.e., “coil current”) for the first power setting is I₁. The firstpower setting is known to not cause plasma ignition, and this can beverified by confirming that the phase difference as measured by VI probe152 is close to −90 degrees. Next, a second power setting will be usedto identify a second plot point 504 on the graph 500. The second powersetting is provided to the process chamber 102 by RF power source 150.This second power setting is greater than the first power setting, butis still known to not cause plasma ignition. The second plot point 504corresponds to voltage V₂ and the measured coil current for the appliedsecond power setting corresponds to I₂. Again, the second power settingcan be verified to not be generating a plasma by confirming that thephase difference is close to −90 degrees. At this point, the first plotpoint 502 and the second plot point 504 can be used to identify thedividing line 506, i.e., a baseline. The dividing line 506 provides plotpoints that represent the base reading measurement 174 a for voltage andcurrent measurements for no-plasma condition within the wafer cavity160.

With the dividing line 506 set for the plasma chamber 102, it is nowpossible to use the coil sensor 116 to measure a current valueconducting through the base 110 a of the lower electrode 110 of theprocess chamber 102 during operation with a third power level (e.g., apower level used during one or more processing operations). The coilcurrent for the third power level is measured and used to verify ifplasma is ignited in the wafer cavity during a plasma process operation.For example, at plot point 508, it can be determined that the voltage ofthe RF power supplied to the process chamber 102 was V₃, and the coilcurrent I₃ measured by the coil sensor 116 is about 13 amps (A).Comparing the values of the voltage V₃ and coil current I₃ of plot point508 against the values of the plot points on the dividing line 506, itcan be determined that no plasma is ignited in the wafer cavity 160.This can be further verified by confirming that the phase difference asmeasured by the VI probe 152 is close to −90 degrees.

In another example, plot point 510 corresponds to voltage V₄ for thethird power level applied to the process chamber 102 and the coilcurrent I₄ measured is about 14 A. Comparing the values of the voltageV₄ and coil current I₄ corresponding to plot point 510 against thevalues related to the plot points on the dividing line 506, it can bedetermined that plasma is ignited in the wafer cavity 160.

It is to be noted that not all voltage, coil current values above acertain value cause ignition of plasma in the wafer cavity 160.Similarly, not all voltage, coil current values that are low relate tonon-plasma condition in the wafer cavity 160. It can be confirmed thatplasma ignition occurs in the wafer cavity 160 for the voltage and coilcurrent values that are low so long as the voltage and coil currentvalues are above the voltage, current values corresponding to the plotpoints of the slope of the dividing line 506. Similarly, it can beconfirmed that no plasma is ignited in the wafer cavity 160 for thevoltage and coil current values that are below the voltage, currentvalues corresponding to the plot points of the slope of the dividingline 506. For example, consider plot point 512 corresponding to voltageV₅, which results in the sensed coil current I₅ of about 8 A. Althoughthe sensed coil current I₅ is low in value, it is above the plot pointsrelated to the slope of the dividing line 506. As a result, the sensedcoil current I₅ would confirm plasma ignition in the wafer cavity 160.The low coil current sensed by the coil sensor 116, for example, may bedue to low density of the plasma ignited in the wafer cavity 160, whichmay be due to low RF power applied to the process chamber 102.

In another example, when the sensed coil current value is high, theplasma may still not be ignited in the wafer cavity 160. Consider plotpoint 514 corresponding to voltage V₆, which results in the sensed coilcurrent I₆ of about 15 A. Although the coil current I₆ sensed by thecoil sensor 116 is high, no plasma is ignited in the process chamber 102as the voltage V₆ and the coil current I₆ values corresponding to plotpoint 514 fall below the corresponding plot points of the dividing line506. Thus, based on the measurements from the coil sensor 116, plasmaignition can be determined.

In an alternative embodiment, it is possible to identify the dividingline 506 slope using data obtained from a network analyzer. Of example,the network analyzer can be used to sense and measure the dark impedanceassociated with capacitance C1 and C2 detected in the process chamber102. The measurements made by the network analyzer can then be used toderive a slope of the dividing line 506. Once the dividing line 506 isfound for the process chamber 102, subsequent measurements made usingthe coil sensor 116 can be used to make determinations as to whetherplasma is ignited or not ignited in the wafer cavity 160 for the powersetting applied to the process chamber 102. The measurements obtainedfrom the coil sensor can be used to assess station-to-station andtool-to-tool matching. Station or tool matching may be achieved, in oneembodiment, by matching the RF characteristics measured by the coilsensor 116 and the VI probe 152 at different stages of the depositionprocess of one station or tool with that of another station or tool toobtain similar plasma conditions within the respective stations ortools. In this embodiment, the measurement from the VI probe 152 may beused to determine base reading measurement of RF characteristics for theprocess chamber 102. Once the base reading measurement of RFcharacteristics are determined for non-plasma condition, measurementfrom coil sensor 116 obtained at different stages of the depositionprocess may be compared to the base reading measurement of RFcharacteristics to determine plasma ignition. The matching ofmeasurement obtained from the coil sensor and verifying against themeasurement from the VI probe ensures verification of plasmarepeatability during the deposition process at different stations withinthe same process chamber or in different process chambers, or usingdifferent tools.

As noted in the various embodiments, the plasma generated within theprocess chamber may be correctly detected by measuring RF current at abase of the lower electrode using the coil sensor. Relying just on theRF characteristics, such as voltage, current measurement, etc., measuredby the VI probe would not accurately determine ignition of plasma in theprocess chamber. This may be attributed to the fact that the voltage,current measured near the RF power input at the powered upper electrodeby the VI probe includes not only the RF characteristics related to theRF power flowing through the wafer cavity, but also RF characteristicsdue to any RF path between the VI probe and ground. Accuratelydetermining plasma ignition in the wafer cavity of the process chambersis critical especially for the process chambers that do not provide anyvisual or optical access to the wafer cavity and when the parasiticcapacitance is comparable with the capacitance of the wafer cavity. Themeasurements obtained from the coil sensor and comparing them withmeasurement obtained using the VI probe can accurately confirm ignitionof plasma in the wafer cavity. The phase difference measurements fromthe VI probe may be used to additionally verify plasma ignition in thewafer cavity.

When intensity of parasitic plasma is non-negligible or when a magnitudeof parasitic capacitance is comparable to capacitance of the wafercavity, just matching the RF characteristic measurements, obtainedthrough a VI probe, of a first processing station with that of a secondprocessing station would not result in matched properties for the plasmaignited in the wafer cavity of the respective first and the secondprocessing stations. This is due to the fact that the VI probe measuresboth the conduction current (i.e., RF current conducting through thewafer cavity) as well as the displacement current (i.e., RF current dueto parasitic capacitive coupling to ground). Such parasitic currentwould cause variation in the plasma properties as the value of theparasitic current is influenced by the variation in the parasitic plasmaand/or parasitic capacitive coupling and is not fully indicative ofplasma ignition conditions within the process chamber. The coil sensorprovides measurements that can be used to more accurately assessstation-to-station or tool-to-tool matching. The VI probe measurements(e.g., phase difference related to voltage and current) may be used toverify the plasma ignition result from the coil sensor measurements. Theaccurate assessment may be attributed to the fact that the coil sensoris able to accurately measure the conduction current through the wafercavity.

In one embodiment, in a multi-processing station process chamber, eachprocessing station may be equipped with its own coil sensor and VI probefor measuring the RF characteristics for the supplied RF power at therespective processing stations. As a result, the RF characteristicmeasurements of a first processing station obtained using a first coilsensor and verified using measurements from a first VI probe can bematched with corresponding RF characteristic measurements of a secondprocessing station obtained using a second coil sensor and a second VIprobe. Such matching would result in a more accurate matching of theproperties of the plasma generated in the wafer cavity at the first andthe second processing stations, respectively. The RF characteristicmeasurements obtained using the coil sensor is not influenced by thevariations due to the parasitic plasma/parasitic capacitance detected inthe process chamber 102. This ensures repeatability of processingcondition within different stations that influences generation andaccurate confirmation of plasma during the deposition process.

FIG. 6 illustrates process operations of a method for measuringoperational parameters of a process chamber, in one embodiment. Themethod begins at operation 610 wherein the process chamber is operatedusing a first power level that is lower than a power required to ignitea plasma in a wafer cavity of the process chamber. A first RFcharacteristic measurement including first current value conductingthrough a base of a lower electrode for a first voltage detected in theprocess chamber is measured during operation of the process chamber withthe first power level, as illustrated in operation 620. The first RFcharacteristic may represent one of a base value reading measurement.The process chamber is operated using a second power level that is lowerthan the power required to ignite the plasma in the wafer cavity, asillustrated in operation 630. A second RF characteristic measurementincluding second current value conducting through the base of the lowerelectrode for a second voltage detected in the process chamber ismeasured during operation of the process chamber with the second powerlevel, as illustrated in operation 640. The second RF characteristic mayrepresent a second one of a base value reading measurement for theprocess chamber. The first the second RF characteristic measurement areused to determine base reading measurement of RF characteristics for theprocess chamber.

The process chamber is operated at a process power level that isdifferent from the first and the second power level. A process currentvalue conducting through the base of the lower electrode is measured forthe process voltage detected in the process chamber during a plasmaprocess operation and a determination is made of when the plasma isignited in the wafer cavity during the plasma process operation bycomparing the process current value against the first and the secondcurrent values defined in the base reading measurement of RFcharacteristics, as illustrated in operation 650. The first, the secondand the process current values are measured by a coil sensor that isdisposed at a base of a lower electrode outside of the process chamberand these measurements are used to confirm plasma presence in the wafercavity. Determination of the plasma ignition in the process chamber maybe verified using phase difference between the voltage and currentdetected in the process chamber, as provided by the VI probe.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications can be practiced within the scope ofthe appended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein, but may be modifiedwithin their scope and equivalents of the claims.

What is claimed is:
 1. A process chamber for detecting formation ofplasma during processing of a semiconductor wafer, the process chambercomprising, an upper electrode, the upper electrode including aplurality of inlets for supplying a gas chemistry to the processchamber, the upper electrode connected to a radio frequency (RF) powersource through a match network to provide RF power to generate a plasma;a lower electrode for supporting the semiconductor wafer, the lowerelectrode is disposed within the process chamber so as to define a wafercavity between a surface of the upper electrode and a top surface of thelower electrode, wherein the lower electrode is electrically grounded;and a coil sensor disposed at a base of the lower electrode that extendsoutside the process chamber, the coil sensor disposed to substantiallysurround the base of the lower electrode, the coil sensor configured tomeasure characteristics of RF current conducting through the wafercavity and to exclude current due to parasitic plasma and parasiticcapacitive coupling to ground, the characteristics of RF current used toconfirm generation of the plasma within the wafer cavity.
 2. The processchamber of claim 1, further includes a voltage-current probe disposedoutside of the process chamber, between the RF power source and theupper electrode to measure characteristics of the RF power delivered tothe process chamber.
 3. The process chamber of claim 1, further includesa ring disposed at an outer periphery of the surface of the upperelectrode, the ring defining a pocket in the wafer cavity tosubstantially contain the plasma.
 4. The process chamber of claim 3,wherein the ring is made of ceramic material.
 5. The process chamber ofclaim 1, wherein the upper electrode functions as a showerhead.
 6. Theprocess chamber of claim 1, wherein one end of the coil sensor iscoupled to an input-output controller, the input-output controller iscommunicatively connected to a user interface of a computing device soas to render information associated with characteristics of the RFcurrent measured by the coil sensor.
 7. The process chamber of claim 1,further includes an edge ring disposed adjacent to the wafer, whenpresent, and configured to surround the wafer, wherein the edge ring ismade of ceramic material.
 8. The process chamber of claim 1, wherein thecoil sensor is an induction coil-based sensor.
 9. A process chamber,comprising, an upper electrode coupled to a radio frequency (RF) powersupply; a lower electrode coupled to ground, wherein a wafer cavity isdefined between the upper electrode and the lower electrode; a basecoupled to the lower electrode, the base is configured to extend intothe process chamber from below the process chamber, such that the basehas an inner portion that is inside the process chamber and an outerportion that is outside the process chamber; a circular channel definedaround the outer portion of the base; and a coil sensor disposed in thecircular channel so that the coil sensor substantially surrounds theouter portion of the base, wherein a first end of the coil sensor isconnected to an input-output controller and a second end of the coilsensor is proximate to the first end when the coil sensor is disposed inthe circular channel.
 10. The process chamber of claim 9, wherein thecoil sensor forms a loop around the outer portion of the base.
 11. Theprocess chamber of claim 9, wherein the coil sensor has an innerconductor extending from the first end to the second end and a wrappingconductor that returns from the second end to the first end, such thatthe inner conductor and the wrapping conductor both terminate at thefirst end.
 12. The process chamber of claim 9, wherein the coil sensoris flexible, such that the coil sensor can be inserted into the circularchannel so that the second end wraps around an inside of the circularchannel.
 13. The process chamber of claim 9, wherein the first end ofthe coil sensor is connected to a coaxial connector that interfaces withthe input-output controller.
 14. The process chamber of claim 9, whereinthe circular channel is disposed above a bellows that surrounds aportion of the outer portion of the base.
 15. The process chamber ofclaim 9, wherein the circular channel surrounds a dielectric O-ring. 16.The process chamber of claim 9, wherein the circular channel is locatedbelow a base of the chamber, outside of the chamber.
 17. The processchamber of claim 9, wherein the coil sensor is configured to measure acurrent conducting through the base.
 18. The process chamber of claim17, wherein the current conducting through the base, as measured by thecoil sensor is compared to saved current measurements to determine whena plasma is ignited within the wafer cavity.